For example, how do we know that the Iceman, whose frozen body was chipped out of glacial ice in 1991, is 5,300 years old?
They release radiation until they eventually become stable isotopes of lead.
Carbon-14 is a radioactive isotope used to date organic material.
Its consistent rate of decay allows the age of an object to be determined by the proportion of carbon-14 to other carbon isotopes. Carbon-14 is also used as a radioactive tracer for medical tests.
Human remains, fossils and organic materials from archaeological sites are all dated using carbon-14.
Books, clothing and food remains are all archaeological artifacts that can be carbon dated.